Astrophysics and Astronomy Commons^™

Comparative Study Of High-Order Positivity-Preserving Weno Schemes, D. V. Kotov, Helen C. Yee, Bjorn Sjögreen

United States National Aeronautics and Space Administration: Publications

In gas dynamics and magnetohydrodynamics flows, physically, the density ρ and the pressure p should both be positive. In a standard conservative numerical scheme, however, the computed internal energy is obtained by subtracting the kinetic energy from the total energy, resulting in a computed p that may be negative. Examples are problems in which the dominant energy is kinetic. Negative ρ may often emerge in computing blast waves. In such situations the computed eigenvalues of the Jacobian will become imaginary. Consequently, the initial value problem for the linearized system will be ill posed. This explains why failure of preserving positivity …

Astr 403: Galactic And Extragalactic Astronomy, Edward Schmidt

Department of Physics and Astronomy: Syllabi

Syllabus for ASTR 403 Galactic and Extragalactic Astronomy for Fall 2011 semester.

High Order Finite Difference Methods With Subcell Resolution For Advection Equations With Stiff Source Terms, Wei Wang, Chi-Wang Shu, H.C. Yee, Björn Sjögreen

United States National Aeronautics and Space Administration: Publications

A new high order finite-difference method utilizing the idea of Harten ENO subcell resolution method is proposed for chemical reactive flows and combustion. In reaction problems, when the reaction time scale is very small, e.g., orders of magnitude smaller than the fluid dynamics time scales, the governing equations will become very stiff. Wrong propagation speed of discontinuity may occur due to the underresolved numerical solution in both space and time. The present proposed method is a modified fractional step method which solves the convection step and reaction step separately. In the convection step, any high order shock-capturing method can be …

Astr 404

Department of Physics and Astronomy: Syllabi

No abstract provided.

Astr 403

Department of Physics and Astronomy: Syllabi

No abstract provided.

Astr 404: Stellar Astrophysics, Edward Schmidt

Department of Physics and Astronomy: Syllabi

Syllabus for ASTR 404: Stellar Astrophysics for Spring 2011 semester.

High-Order Finite Difference Methods With Subcell Resolution For 2d Detonation Waves, W. Wang, C.-W. Shu, Helen Yee, Bjorn Sjögreen

United States National Aeronautics and Space Administration: Publications

In simulating hyperbolic conservation laws in conjunction with an inhomogeneous stiff source term, if the solution is discontinuous, spurious numerical results may be produced due to the different time scales of the transport part and the source term. This numerical issue often arises in combustion and high-speed chemical reacting flows.

Our objective in this study is to extend this method to two-dimensional reactive Euler equations. The first step of the proposed fractional step method is the convection step which solves the homogeneous hyperbolic conservation law in which any high-resolution shock-capturing method can be used. The aim in this step is …

Variable High-Order Overset Grid Methods For Mixed Steady And Unsteady Multiscale Viscous Hypersonic Nonequilibrium Flows, A. Lani, Bjorn Sjögreen, Helen Yee, W, D. Henshaw

United States National Aeronautics and Space Administration: Publications

The objective of the current paper † is a further validation of the overset grid capability for high-speed chemical nonequilibrium flows. The current investigation, which is a follow-up on previous work by (Sj¨ogreen & Yee 2009b), (Lani et al. 2010a), (Wang et al. 2009), (Wang et al. 2010), (Lani et al. 2010b), extends the use of variable order methods for both inviscid and viscous chemical nonequilibrium flows with strong shocks on 2D and 3D multiblock overlapping grids. A 5-species and one-temperature air model in chemical nonequilibrium is considered in all cases. Second-order TVD, fifth- or higher-order WENO schemes are applied …

High-Order Finite Difference Methods With Subcell Resolution For Hyperbolic Conservation Laws With Stiff Reaction Terms: Preliminary Results, W. Wang, C.-W. Shu, Helen Yee, Bjorn Sjögreen

United States National Aeronautics and Space Administration: Publications

The motivation for this research stems from the high-speed chemical reacting flows which have stiff reaction terms, where the chemical time scales are often much smaller than the fluid dynamics time scales. It is usually too expensive to resolve all the spatial/ temporal scales if we are only interested in the main flow. On the other hand, insufficient spatial/temporal resolution will cause the speed of propagation of discontinuities to be incorrectly predicted for many numerical methods. This numerical phenomenon was first observed by Colella et al. (1986). Then LeVeque & Yee (1990) showed that a similar spurious propagation phenomenon can …

High-Order Simulation Of Hypersonic Nonequilibrium Flows On Overset Grids, A. Lani, Bjorn Sjögreen, Helen Yee

United States National Aeronautics and Space Administration: Publications

The time-accurate unsteady 3D compressible flow solver ADPDIS3D is supported by a grant from the Department of Energy (DOE) SciDAC program through the Science Application Partnership (SAP) initiative. The objective of this grant is to develop, implement and validate this variable high-order 3-D multiblock overlapping (overset) grid solver for turbulence with strong shocks and density variations. ADPDIS3D includes capabilities for both direct numerical simulation (DNS), resolving all scales of the flow fields, and large eddy simulation (LES) modeling the small turbulent scales. One of the unique features of the code is the ability to perform DNS and LES computations in …

High Order Well-Balanced Schemes And Applications To Non-Equilibrium Flow With Stiff Source Terms, Wei Wang, Chi-Wang Shu, H. C. Yee, Björn Sjögreen

United States National Aeronautics and Space Administration: Publications

The stiffness of the source terms in modeling non-equilibrium ow problems containing finite-rate chemistry or combustion poses additional numerical difficulties beyond that for solving non-reacting flows. A well-balanced scheme, which can preserve certain non-trivial steady state solutions exactly, may help minimize some of these difficulties. In this paper, a simple one dimensional non-equilibrium model with one temperature is considered. We first describe a general strategy to design high order well-balanced finite difference schemes and then study the well-balanced properties of the high order finite difference weighted essentially non-oscillatory (WENO) scheme, modified balanced WENO schemes and various TVD schemes. The advantages …

On Well-Balanced Schemes For Non-Equilibrium Flow With Stiff Source Terms, W. Wang, C.-W. Shu, Helen Yee

United States National Aeronautics and Space Administration: Publications

In the modeling of unsteady reactive problems, the interaction of turbulence with finiterate chemistry introduces a wide range of space and time scales, leading to additional numerical difficulties. A main difficulty stems from the fact that most numerical algorithms used in reacting flows were originally designed to solve non-reacting fluids. As a result, spatial stiffness due to reacting source terms and turbulence/chemistry interaction are major stumbling blocks to numerical algorithm development. One of the important numerical issues is the proper numerical treatment of a system of highly coupled stiff non-linear source terms, which will result in possible spurious steady state …

Agn Reddening And Ultraviolet Extinction Curves From Hubble Space Telescope Spectra, C. Martin Gaskell, A. J. Benkler

C. Martin Gaskell Publications

We present intrinsic extinction curves for 14 AGNs. The AGNs have reddenings, E(B-V), of up to 0.36 mag. The majority (13 out of 14) of the extinction curves are not steep in the UV. Of the seven best determined extinction curves, five have extinction curves that are as flat as the standard Galactic curve in the optical and near UV, but flatter in the far UV, and without the λ2175 feature. One AGN, B3 0754+394, has a steep SMC-like extinction curve, and another, Mrk 304, has an LMC-like extinction curve, including a probable λ2175 bump. The remaining seven, lower-quality, extinction …

The Cosmic Ray Observatory Project: A Statewide Outreach And Education Ex-Periment In Nebraska, Daniel Claes, Gregory Snow

Gregory Snow Publications

Abstract: The Cosmic Ray Observatory Project (CROP) is a statewide education and research ex-periment involving Nebraska high school students, teachers and university undergraduates in the study of extensive cosmic-ray air showers. A network of high school teams construct, install, and op-erate school-based detectors in coordination with University of Nebraska physics professors and graduate students. The detector system at each school is an array of scintillation counters recycled from the Chicago Air Shower Array in weather-proof enclosures on the school roof, with a GPS re-ceiver providing a time stamp for cosmic-ray events. The detectors are connected to triggering elec-tronics and a …

Results From The Dc-8 Inlet Characterization Experiment (Dice): Airborne Versus Surface Sampling Of Mineral Dust And Sea Salt Aerosols, Cameron S. Mcnaughton, Antony D. Clarke, Steven G. Howell, Mitchell Pinkerton, Bruce Anderson, Lee Thornhill, Charlie Hudgins, Edward Winstead, Jack E. Dibb, Eric Scheuer, Hal Maring

United States National Aeronautics and Space Administration: Publications

During May and June of 2003 NASA conducted the DC-8 Inlet Characterization Experiment (DICE). The study was undertaken to quantify the performance of three passive, solid diffuser inlets used aboard the DC-8 aircraft to sample optically effective aerosol sizes. Aerosol optical properties measured behind the University of Hawai’i (UH) and the University of New Hampshire (UNH) inlets were within 10% of the ground based measurements whereas the NASA Langley (LaRC) inlet reduced scattering values for supermicrometer dust by approximately 50%. Based on the DICE results the aerodynamic 50% passing efficiency of the inlets and transport plumbing is determined to be …

Optical Variability Of The Three Brightest Nearby Quasars, C. Martin Gaskell, Andrew J. Benker, Jeffrey S. Campbell, Thomas A. George, Cecilia H. Hedrick, Mary E. Hiller, Elizabeth S. Klimek, Joseph P. Leonard, Shoji Masatoshi, Bradley W. Peterson, Kelly S. Peterson, Kelly M. Sanders

C. Martin Gaskell Publications

We report on the relative optical variability of the three brightest nearby quasars, 3C 273, PDS 456, and PHL 1811. All three have comparable absolute magnitudes, but PDS 456 and PHL 1811 are radio quiet. PDS 456 is a broadline object, but PHL 1811 could be classified as a high-luminosity Narrow-Line Seyfert 1 (NLS1). Both of the radio-quiet quasars show significant variability on a timescale of a few days. The seasonal rms V-band variability amplitudes of 3C 273 and PDS 456 are indistinguishable, and the seasonal rms variability amplitude of PHL 1811 was only exceeded by 3C 273 once in …

Nonlinear Filtering In Compact High-Order Schemes, H. C. Yee, Björn Sjögreen

United States National Aeronautics and Space Administration: Publications

The adaptive nonlinear filtering approach for shock/turbulence gas dynamics and magnetohydrodynamics (MHD) flows adopted in our previous work is employed in conjunction with compact high-order methods as the spatial base scheme. The objective is to compare the performance of nonlinear filtering in compact high-order schemes with nonlinear filtering in standard central (non-compact) schemes for multiscale problems containing shock waves.

Entropy Splitting For High Order Numerical Simulation Of Vortex Sound At Low Mach Numbers, Bernhard Müller, H. C. Yee

United States National Aeronautics and Space Administration: Publications

Several recent developments in efficient, stable, highly parallelizable high order non-dissipative spatial schemes with characteristic based filters that exhibit low dissipation for long time linear and nonlinear wave propagations are utilized for computational aeroacoustics (CAA). For stability consideration, the Euler equations are split into a conservative and a symmetric non-conservative portion. Due to the large disparity of acoustic and stagnation quantities in low Mach number aeroacoustics, the split Euler equations are formulated in perturbation form to minimize numerical cancellation errors. Spurious oscillations are suppressed by a characteristic-based filter. The method has been applied to accurately simulate the sound emitted by …

Designing Adaptive Low-Dissipative High Order Schemes For Long-Time Integrations, Helen Yee, Bjorn Sjögreen

United States National Aeronautics and Space Administration: Publications

A general framework for the design of adaptive low-dissipative high order schemes is presented. It encompasses a rather complete treatment of the numerical approach based on four integrated design criteria: (1) For stability considerations, condition the governing equations before the application of the appropriate numerical scheme whenever it is possible. (2) For consistency, compatible schemes that possess stability properties, including physical and numerical boundary condition treatments, similar to those of the discrete analogue of the continuum are preferred. (3) For the minimization of numerical dissipation contamination, efficient and adaptive numerical dissipation control to further improve nonlinear stability and accuracy should …

Building Blocks For Reliable Complex Nonlinear Numerical Simulations, Helen Yee

United States National Aeronautics and Space Administration: Publications

This chapter describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is …

Entropy Splitting For High Order Numerical Simulation Of Vortex Sound At Low Mach Numbers, B. Müller, H.C. Yee

United States National Aeronautics and Space Administration: Publications

A method of minimizing numerical errors, and improving nonlinear stability and accuracy associated with low Mach number computational aeroacoustics (CAA) is proposed. The method consists of two levels.

Science On The Great Plains: The History Of Physics And Astronomy At The University Of Nebraska-Lincoln, M. Eugene Rudd

M. Eugene Rudd Publications

The year 1988 marked the 100th anniversary of the founding of the Department of Physics at the University of Nebraska. While the year passed without fanfare in the department, DuaneJaecks, one of the members of the faculty, suggested to the author that it would be a good time to write a history of what is now the Department of Physics and Astronomy. He not only provided the initial impetus for the project, but has also given it his continual help and encouragement. While the initial plan was to write only a brief, informal departmental history, the project, like Topsy, grew. …

Semi-Implicit And Fully Implicit Shock-Capturing Methods For Nonequilibrium Flows, Helen C. Yee, Judy L. Shinn

United States National Aeronautics and Space Administration: Publications

Some numerical aspects of finite-difference algorithms for nonlinear multidimensional hyperbolic conservation laws with stiff nonhomogeneous (source) terms are discussed. If the stiffness is entirely dominated by the source term, a semi-implicit shock-capturing method is proposed. However, if the stiffness is not solely dominated by the source terms, a fully implicit method would be a more efficient solution procedure. The primary motivation for constructing these schemes was to address large systems of thermally and chemically nonequilibrium flows in the hypersonic regime. Due to the unique structure of the eigenvalues and eigenvectors for fluid flows of this type, the computation can be …

A Class Of High-Resolution Explicit And Implicit Shock-Capturing Methods, Helen C. Yee

United States National Aeronautics and Space Administration: Publications

The development of shock-capturing finite difference methods for hyperbolic conservation laws has been a rapidly growing area for the last decade. Many of the fundamental concepts, state-of-the-art developments and applications to fluid dynamics problems can only be found in meeting proceedings, scientific journals and internal reports. This paper attempts to give a unified and generalized formulation of a class of high-resolution, explicit and implicit shockcapturing methods, and to illustrate their versatility in various steady and unsteady complex shock waves, perfect gases, equilibrium real gases and nonequilibrium flow computations. These numerical methods are formulated for the purpose of ease and efficient …

Upwind And Symmetric Shock- Capturing Schemes, H.C. Yee

United States National Aeronautics and Space Administration: Publications

The development of numerical methods for hyperbolic conservation laws has been a rapidly growing area for the last ten years. Many of the fundamental concepts and state-of-the-art developments can only be found in meeting proceedings or internal reports. This review paper attempts to give an overview and a unified formulation of a class of shock-capturing methods. Special emphasis will be on the construction of the basic nonlinear scalar second-order schemes and the methods of extending these nonlinear scalar schemes to nonlinear systems via the exact Riemann solver, approximate Riemann solvers, and flux-vector splitting approaches. Generalization of these methods to efficiently …

Implicit Tvd Schemes For Hyperbolic Conservation Laws In Curvilinear Coordinates, Helen Yee, A. Harten

United States National Aeronautics and Space Administration: Publications

A one-parameter family of explicit and implicit upwind second-order-accurate, total variation diminishing (TVD) schemes has been developed by Harten. These TVD schemes have the property of not generating spurious oscillations when applied to one-dimensional nonlinear scalar hyperbolic conservation laws and constant coefficient hyperbolic systems. The goal of this work is to extend these methods to the multidimensional hyperbolic conservation laws in curvilinear coordinates. Various ways of linearizing the implicit operator and solution strategies to improve the computation efficiency of the implicit algorithm are discussed. Numerical experiments with some AGARD test cases for steady-state airfoil calculations show that the proposed linearized …

Civilian Space Stations And The U.S. Future In Space, U.S. Office Of Technology Assessment

Space Law Documents

After the expenditure of some $200 billion (1984$) since the launch of its first spacecraft in early 1958, the United States has obtained the scientific knowledge and developed the technological capability and professional expertise to succeed in virtually any theoretically possible civilian space venture that it may choose to undertake, But America’s second quarter-century of space activities promises to differ markedly from the first, almost wholly exploratory, era. If space is to be successfully developed in roughly the same fashion as have other, more familiar natural resources and environments, the next stage will be characterized by establishing and securing the …

Implicit Total Variation Diminishing (Tvd) Schemes For Steady-State Calculations, H. C. Yee, R. F Warming, A. Harten

United States National Aeronautics and Space Administration: Publications

We examine the application of a new implicit unconditionally-stable high-resolution TVD scheme to steady-state calculations. It is a member of a one-parameter family of explicit and implicit second-order accurate schemes developed by Harten for the computation of weak solutions of one-dimensional hyperbolic conservation laws. This scheme is guaranteed not to generate spurious oscillations for a nonlinear scalar equation and a constant coefficient system. Numerical experiments show that this scheme not only has a fairly rapid convergence rate, but also generates a highly-resolved approximation to the steady-state solution. A detailed implementation of the implicit scheme for the one- and two-dimensional compressible …

Boundary Approximations For Implicit Schemes For .One-Dimensional Inviscid Equations Of Gasdynamics, Helen Yee, R. M. Beam, R. F. Warming

United States National Aeronautics and Space Administration: Publications

The applicability to practical calculations of recent theoretical developments in the stability analysis of difference approximations is examined for initial boundary-value problems of the hyperbolic type. For the numerical experiments the one-dimensional inviscid gasdynamic equations in conservation law form are selected. A class of implicit schemes based on linear multistep methods for ordinary differential equations is chosen and the use of space or space-time extrapolations as implicit or explicit boundary schemes is emphasized. Some numerical examples with various inflow-outflow conditions highlight the commonly discussed issues: explicit vs implicit boundary schemes, and unconditionally stable schemes.

Civilian Space Policy And Applications, U.S. Office Of Technology Assessment

Space Law Documents

The United States orbited its first satellite in 1958, nearly a quarter century ago. In the intervening years, the United States has made great strides in developing peaceful and practical uses of space technology. However, in spite of the dramatic successes of the space program, among which are the recent flights of the Columbia shuttle orbiter, many informed observers express considerable unease about the future of our civilian efforts in space, particularly in light of increased foreign competition and stringent fiscal restraints.

Because of these uncertainties and also because of emerging new prospects for using the space environment, this assessment …